Exhaust plenum for radial diffuser

ABSTRACT

An exhaust gas diffuser for a turbomachine includes a diffuser supported on a turbine rotor, aligned with an axis of said turbine rotor. The diffuser is configured to re-direct turbine exhaust gas substantially ninety degrees from a first direction of flow along the rotor axis. A plenum chamber is in fluid communication with and surrounds an outlet end of the diffuser. The plenum chamber is in fluid communication with a transition duct adapted to supply the exhaust gas to another turbomachine. The plenum chamber expands in volume between the diffuser and the transition duct.

BACKGROUND OF THE INVENTION

This invention relates generally to integrating heat recovery steam generation (HRSG) systems with gas turbine exhaust components, and more specifically, to a turbine exhaust gas plenum designed to promote uniform flow of combustion gases into the HRSG.

In combined cycle power generation systems, heated exhaust gas discharged from gas turbines may be used by HRSG systems as a source of heat which may be transferred to a water source to generate superheated steam. In turn, the superheated steam may be used within steam turbines as a source of power. The heated exhaust gas from a gas turbine may be delivered to the HRSG system through, among other things, an exhaust plenum and diffuser, which may help convert the kinetic energy of the heated exhaust gas exiting the last stage of the gas turbine into potential energy in the form of increased static pressure. Once delivered to the HRSG system, the heated exhaust gas may traverse a series of heat exchanger elements, such as superheaters, re-heaters, evaporators, economizers, and so forth. The heat exchanger elements may be used to transfer heat from the heated exhaust gas to the water source to generate superheated steam. It is a design objective to promote uniform flow through the exhaust gas plenum without negatively impacting diffuser performance, i.e., enabling flow diffusion without appreciable total pressure loss.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, there is provided an exhaust gas diffuser for a turbomachine comprising a diffuser supported in a turbine rotor, aligned with an axis of the turbine rotor, the diffuser configured to re-direct turbine exhaust gas substantially ninety degrees from a first direction of flow along the axis; a plenum chamber in fluid communication with and surrounding an outlet end of the diffuser, the plenum chamber in fluid communication with a transition duct adapted to supply the exhaust gas to another turbomachine; wherein the plenum chamber expands in volume in a direction toward the transition duct.

In another embodiment, there is provided a turbomachine comprising a gas turbine section including a turbine rotor; a radial diffuser disposed along a first axis of the turbine rotor; an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, the exhaust plenum extending along a second axis substantially perpendicular to the first axis, the plenum chamber expanding in volume along the second axis.

In still another embodiment, there is provided a combined cycle system comprising: a gas turbine including a turbine rotor extending along a first axis; a heat recovery steam generator; a steam turbine adapted to receive steam from the heat recovery steam generator; a radial diffuser disposed along the first axis; and an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, the exhaust plenum extending along a second axis substantially perpendicular to the first axis, the plenum chamber expanding in volume along the second axis and communicating with the heat recovery steam generator.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic flow diagram of an embodiment of a combined cycle power generation system having a gas turbine, a steam turbine, and an HRSG;

FIG. 2 is a detailed but partial side section view of an embodiment of the gas turbine of FIG. 1 having heat exchanger elements of the HRSG of FIG. 1 integrated with components of an exhaust diffuser of the gas turbine;

FIG. 3 is a cut-away perspective view of an exhaust gas plenum of the type which could be employed in the gas turbine of FIG. 2;

FIG. 4 is a partially cut-away top view of the exhaust plenum shown in FIG. 3;

FIG. 5 is a perspective view of an exhaust gas diffuser and plenum in accordance with an exemplary but nonlimiting embodiment of the invention;

FIG. 6 is another perspective view of the exhaust gas diffuser and plenum shown in FIG. 5; and

FIG. 7 is a top plan view of the exhaust gas diffuser and plenum shown in FIGS. 5 and 6.

FIG. 8 illustrates HRSG inlet profiles at the plenum exit and at the downstream edge of the transition section.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters are not exclusive of other parameters of the disclosed embodiments.

FIG. 1 is a schematic flow diagram of an embodiment of a combined cycle power generation system 10 having a gas turbine, a steam turbine, and an HRSG. Specifically, the system 10 may include a gas turbine 12 for driving a first load 14. The first load 14 may be, for instance, an electrical generator for producing electrical power. The gas turbine 12 may include a turbine 16, a combustor 18, and a compressor 20. The system 10 may also include a steam turbine 22 for driving a second load 24. The second load 24 may also be an electrical generator for generating electrical power. It will be understood, however, that both the first and second loads 14, 24 may be other types of loads capable of being driven by the gas turbine 12 and steam turbine 22. In addition, although the gas turbine 12 and steam turbine 22 may drive separate loads 14 and 24, as shown in the illustrated embodiment, the gas turbine 12 and steam turbine 22 may also be utilized in tandem to drive a single load via a single shaft. In the illustrated embodiment, the steam turbine 22 may include one low-pressure section 26 (LP ST), one intermediate-pressure section 28 (IP ST), and one high-pressure section 30 (HP ST). However, the specific configuration of the steam turbine 22, as well as the gas turbine 12, may be implementation-specific and may include any combination of sections and/or stages.

The system 10 may also include a multi-stage HRSG 32. The simplified depiction of the HRSG 32 and its components are not intended to be limiting. Rather, the illustrated HRSG 32 is shown to convey the general arrangement of such systems. Heated exhaust gas 34 from the gas turbine 12 may be transported into the HRSG 32 and used to heat steam used to power the steam turbine 22. Exhaust from the low-pressure section 26 of the steam turbine 22 may be directed into a condenser 36. Condensate from the condenser 36 may, in turn, be directed into a low-pressure section of the HRSG 32 with the aid of a condensate pump 38.

The condensate may then flow through a low-pressure economizer 40 (LPECON), which is a device configured to heat feedwater with gases, may be used to heat the condensate. From the low-pressure economizer 40, the condensate may either be directed into a low-pressure evaporator 42 (LPEVAP) or to an intermediate-pressure economizer 44 (IPECON). Steam from the low-pressure evaporator 42 may be returned to the low-pressure section 26 of the steam turbine 22. Likewise, from the intermediate-pressure economizer 44, the condensate may either be directed into an intermediate-pressure evaporator 46 (IPEVAP) or to a high-pressure economizer 48 (HPECON). In addition, steam from the intermediate-pressure economizer 44 may be sent to a fuel gas heater (not shown) where the steam may be used to heat fuel gas for use in the combustor 18 of the gas turbine 12. Steam from the intermediate-pressure evaporator 46 may be sent to the intermediate-pressure section 28 of the steam turbine 22.

Finally, condensate from the high-pressure economizer 48 may be directed into a high-pressure evaporator 50 (HPEVAP). Steam exiting the high-pressure evaporator 50 may be directed into a primary high-pressure superheater 52 and a finishing high-pressure superheater 54, where the steam is superheated and eventually sent to the high-pressure section 30 of the steam turbine 22. Exhaust from the high-pressure section 30 of the steam turbine 22 may, in turn, be directed into the intermediate-pressure section 28 of the steam turbine 22, and exhaust from the intermediate-pressure section 28 of the steam turbine 22 may be directed into the low-pressure section 26 of the steam turbine 22.

An inter-stage attemperator 56 may be located in between the primary high-pressure superheater 52 and the finishing high-pressure superheater 54. The inter-stage attemperator 56 may allow for more robust control of the exhaust temperature of steam from the finishing high-pressure superheater 54.

In addition, exhaust from the high-pressure section 30 of the steam turbine 22 may be directed into a primary re-heater 58 and a secondary re-heater 60 where it may be re-heated before being directed into the intermediate-pressure section 28 of the steam turbine 22. The primary re-heater 58 and secondary re-heater 60 may also be associated with an inter-stage attemperator 62 for controlling the exhaust steam temperature from the re-heaters.

In combined cycle systems such as system 10, hot exhaust may flow from the gas turbine 12 and pass through the HRSG 32 and may be used to generate high-pressure, high-temperature steam. The steam produced by the HRSG 32 may then be passed through the steam turbine 22 for power generation. In addition, the produced steam may also be supplied to any other processes where superheated steam may be used. The gas turbine 12 generation cycle is often referred to as the “topping cycle,” whereas the steam turbine 22 generation cycle is often referred to as the “bottoming cycle.” By combining these two cycles as illustrated in FIG. 1, the combined cycle power generation system 10 may lead to greater efficiencies in both cycles. In particular, exhaust heat from the topping cycle may be captured and used to generate steam for use in the bottoming cycle.

Therefore, one aspect of the combined cycle power generation system 10 is the ability to recapture heat from the heated exhaust gas 34 using the HRSG 32. As illustrated in FIG. 1, components of the gas turbine 12 and the HRSG 32 may be separated into discrete functional units. In other words, the gas turbine 12 may generate the heated exhaust gas 34 and direct the heated exhaust gas 34 toward the HRSG 32, which may be primarily responsible for recapturing the heat from the heated exhaust gas 34 by generating superheated steam. In turn, the superheated steam may be used by the steam turbine 22 as a source of power. The heated exhaust gas 34 may be transferred to the HRSG 32 through ductwork, which may vary based on the particular design of the combined cycle power generation system 10.

A more detailed illustration of how the gas turbine 12 functions may help illustrate how the heated exhaust gas 34 may be transferred to the HRSG 32 from the gas turbine 12. Accordingly, FIG. 2 is a detailed side view of an embodiment of the gas turbine 12 of FIG. 1 having heat exchanger elements of the HRSG 32 of FIG. 1 integrated with components of an exhaust diffuser of the gas turbine 12. As described with respect to FIG. 1, the gas turbine 12 may include the turbine 16, the combustor 18, and the compressor 20. Air may enter through an air intake 64 and be compressed by the compressor 20. Next, the compressed air from the compressor 20 may be directed into the combustor 18 where the compressed air may be mixed with fuel gas. The fuel gas may be injected into the combustor 18 through a plurality of fuel nozzles 66. The mixture of compressed air and fuel gas is generally burned within the combustion chamber of the combustor 18 to generate a high-temperature, high-pressure combustion gas, which may be used to generate torque within the turbine 16. A rotor of the turbine 16 may be coupled to a rotor of the compressor 20, such that rotation of the turbine rotor may also cause rotation of the compressor 20. In this manner, the turbine 16 drives the compressor 20 as well as the load 14 (not shown in FIG. 2). Exhaust gas from the turbine 16 section of the gas turbine 12 may be directed into an exhaust diffuser 68. In the embodiment of FIG. 2, the exhaust diffuser 68 may be a radial exhaust diffuser, whereby the exhaust gas may be re-directed by exit guide vanes 70 to exit the exhaust diffuser 68 through a 90-degree turn outwardly (i.e., radially) through an exhaust plenum (not shown) and a transition inlet to the HRSG 32.

Another aspect of certain components of the exhaust diffuser 68, in addition to directing the heated exhaust gas 34 to the HRSG 32, may be to ensure that certain aerodynamic properties of the heated exhaust gas 34 are achieved. For instance, an exhaust frame strut 72, illustrated in FIG. 2, may be cambered with an airfoil wrapped around it. The exhaust frame strut 72 may also be rotated such that swirling of the heated exhaust gas 34 may be minimized and flow of the heated exhaust gas 34 may generally be more axial in nature until flowing through the exit guide vanes 70. In addition, the exit guide vanes 70 may also be designed in such a way that, when the heated exhaust gas 34 is turned toward the exhaust plenum at a 90-degree angle, the exit guide vanes 70 minimize the aerodynamic loss incurred in turning the flow 90 degrees radially. Therefore, proper aerodynamic design of the exhaust frame strut 72, exit guide vanes 70, as well as other components of the exhaust diffuser 68 within the flow path of the heated exhaust gas 34, may be a design consideration.

FIG. 3 is a cut-away perspective view of an embodiment of a diffuser that may be similar to the diffuser 68 in FIG. 2, but for convenience, it will be appreciated that the diffuser is not shown to the same scale as in FIG. 2. The diffuser 68 connects to a plenum 74 which, along with guide vanes 46, redirects the exhaust gas substantially ninety (90) degrees and into the transition duct 76 which connects to the HRSG inlet (not shown). The radial guide vanes 46 may be circular (e.g., tapered annular or conical structures) and disposed concentrically about the x-axis 31. The plenum 74 then gradually guides the combustion gases along the z-axis 35, into the expanding transition section 76 which is connected to the inlet to the HRSG.

The plenum 74 in the known configuration shown in FIGS. 3 and 4 is generally square or rectangular in shape, but with a slanted end wall portion 78 extending from the top wall 80 to a side wall 82. Walls 80 and 82 are substantially perpendicular to each other, while upstream and downstream sides 84, 86, respectively, are parallel as best seen in FIG. 4. The bottom wall 88 is parallel to the top wall 80, but may have a slanted component 90 between the bottom wall 88 and the side wall 82.

FIGS. 5-7 illustrate a modified plenum 100 in accordance with an exemplary but nonlimiting embodiment of the invention. The radial diffuser 101 is received within the plenum inlet, concentric to the turbine rotor axis 114 (FIG. 7). In this example, the plenum 100 is formed with a radiused end defined by a curved end wall 102 merging with top and bottom walls 104, 106. The curved end wall 102 and top and bottom walls 104, 106 collectively form a peripheral edge wall upstream and downstream side walls 108, 110, respectively, which extend from the radiused end wall 102 to the expanding transition section 112. The curved end wall 102 is drawn on the center axis 114 of the diffuser 101 (here again, not drawn to scale), and the top and bottom walls 104, 106 extend tangentially, in parallel, from opposite ends of the radiused end wall. Note that the straight top and bottom walls 104, 106 cross the axis 114 of the diffuser/turbine rotor.

It will be understood that the internal vane components of the diffuser may be similar to the arrangement shown in FIG. 3.

Significantly, the upstream and downstream side walls 108 and 110 are not parallel. As best seen in FIG. 7, the downstream side wall 110 is perpendicular to the center axis 114, but the upstream side wall 108 extends at an angle of between 20 and 50 degrees (and preferably between 35 and 45 degrees) relative to the downstream side wall 110. This expansion of the flow path from the plenum 100 to the transition section 112 promotes a redistribution to uniform flow of gases to the HRSG inlet without impact on diffuser performance. In fact, the uniform flow not only benefits HRSG performance, but also simplifies the design of the HRSG silencer located in the HRSG inlet. The plenum design described herein also enables relatively flat inlet profiles across operating conditions, and across a range of last stage turbine bucket exit profiles.

FIG. 8 illustrates HRSG inlet profiles at the plenum exit plane 116 and at the downstream edge 118 of the transition section 112. The Y-axis “% Span” refers to the height of the plenum, from bottom to top. It can be seen that the “total Velocity” of air flow through the plenum is relatively uniform across the height of the plenum.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. An exhaust gas diffuser for a turbomachine comprising: a diffuser supported in a turbine rotor, aligned with an axis of said turbine rotor, said diffuser configured to re-direct turbine exhaust gas substantially ninety degrees from a first direction of flow along said axis; a plenum chamber in fluid communication with and surrounding an outlet end of said diffuser, said plenum chamber in fluid communication with a transition duct adapted to supply the exhaust gas to another turbomachine; wherein said plenum chamber expands in volume in a direction toward said transition duct.
 2. The exhaust gas diffuser of claim 1 wherein said plenum chamber is comprised in part of a pair of non-parallel side walls and a peripheral edge wall connecting said pair of non-parallel side walls.
 3. The exhaust gas diffuser of claim 2 wherein one of said pair of non-parallel side walls is substantially perpendicular to said axis.
 4. The exhaust gas diffuser of claim 3 wherein the other of said pair of non-parallel side walls extends at an angle of 20-50° relative to said one of said non-parallel side walls.
 5. The exhaust gas diffuser of claim 3 wherein the other of said pair of non-parallel side walls extends at an angle of 35-45° relative to said one of said non-parallel side walls.
 6. The exhaust gas diffuser of claim 2 wherein said peripheral edge wall comprises a radiused end portion connecting to a pair of straight, substantially parallel top and bottom wall portions.
 7. The exhaust gas diffuser of claim 6 wherein said radiused end portion lies on one side of said axis and said pair of straight, substantially parallel top and bottom wall portions cross said axis, connecting to said transition duct on an opposite side of said axis.
 8. The exhaust gas diffuser of claim 7 wherein the other of said pair of non-parallel side walls extends at an angle of 20-50° relative to said one of said non-parallel side walls.
 9. The exhaust gas diffuser of claim 7 wherein the other of said pair of non-parallel side walls extends at an angle of 35-45° relative to said one of said non-parallel side walls.
 10. A turbomachine comprising: a gas turbine section including a turbine rotor; a radial diffuser disposed along a first axis of said turbine rotor; an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, said exhaust plenum extending along a second axis substantially perpendicular to said first axis, said plenum chamber expanding in volume along said second axis.
 11. The turbomachine of claim 1 wherein said plenum chamber is comprised in part of a pair of non-parallel side walls an a peripheral edge wall connecting said pair of non-parallel side walls.
 12. The turbomachine of claim 11 wherein one of said pair of non-parallel side walls is substantially perpendicular to said axis.
 13. The turbomachine of claim 12 wherein the other of said pair of non-parallel side walls extends at an angle of 20-50° relative to said one of said non-parallel side walls.
 14. The turbomachine of claim 12 wherein the other of said pair of non-parallel side walls extends at an angle of 35-45° relative to said one of said non-parallel side walls.
 15. The turbomachine of claim 11 wherein said peripheral edge wall comprises a radiused end portion connecting to a pair of straight, substantially parallel top and bottom wall portions.
 16. The turbomachine of claim 15 wherein said radiused end portion lies on one side of said axis and said pair of straight, substantially parallel top and bottom wall portions cross said axis, connecting to said transition duct on an opposite side of said axis.
 17. A combined cycle system comprising: a gas turbine including a turbine rotor extending along a first axis; a heat recovery steam generator; a steam turbine adapted to receive steam from said heat recovery steam generator; a radial diffuser disposed along said first axis; and an exhaust plenum comprising an inlet receiving a portion of the radial diffuser, said exhaust plenum extending along a second axis substantially perpendicular to said first axis, said plenum chamber expanding in volume along said second axis and communicating with said heat recovery steam generator.
 18. A combined cycle system of claim 17 wherein said plenum chamber is comprised in part of a pair of non-parallel side walls an a peripheral edge wall connecting said pair of non-parallel side walls and wherein one of said pair of non-parallel side walls is substantially perpendicular to said axis.
 19. A combined cycle system of claim 18 wherein the other of said pair of non-parallel side walls extends at an angle of 20-50° relative to said one of said non-parallel side walls.
 20. A combined cycle system of claim 18 wherein the other of said pair of non-parallel side walls extends at an angle of 35-45° relative to said one of said non-parallel side walls. 